// Book.java (抽象类)
package Object.work.model;

public abstract class Book extends LibraryItem {
    private String author;
    private String isbn;

    public Book(String id, String title, int year, String author, String isbn) {
        super(id, title, year);
        this.author = author;
        this.isbn = isbn;
    }

    // Getters
    public String getAuthor() {
        return author;
    }

    public String getIsbn() {
        return isbn;
    }

    @Override
    public String toString() {
        return super.toString() + ", Author: " + author + ", ISBN: " + isbn;
    }
}